Hydrostatic Strain Research Articles

Large enhancement of superconducting transition temperature in single-element superconducting rhenium by shear strain.

Finding a physical approach for increasing the superconducting transition temperature (Tc) is a challenge in the field of material science. Shear strain effects on the superconductivity of rhenium were investigated using magnetic measurements, X-ray diffraction, transmission electron microscopy, and first-principles calculations. A large shear strain reduces the grain size and simultaneously expands the unit cells, resulting in an increase in Tc. Here we show that this shear strain approach is a new method for enhancing Tc and differs from that using hydrostatic strain. The enhancement of Tc is explained by an increase in net electron–electron coupling rather than a change in the density of states near the Fermi level. The shear strain effect in rhenium could be a successful example of manipulating Bardeen–Cooper–Schrieffer-type Cooper pairing, in which the unit cell volumes are indeed a key parameter.

Anisotropic straining of graphene using micropatterned SiN membranes

We use micro-Raman spectroscopy to study strain in free-standing graphene monolayers anchored to SiN holes of non-circular geometry. We show that a uniform differential pressure load yields measurable deviations from hydrostatic strain, conventionally observed in radially symmetric microbubbles. A pressure load of 1 bar yields a top hydrostatic strain of ≈ 0.7% and a G± splitting of 10 cm−1 in graphene clamped to elliptical boundaries with axes 40 and 20 μm, in good agreement with the calculated anisotropy Δε ≈ 0.6% and consistently with recent reports on Grüneisen parameters. The implementation of arbitrary strain configurations by designing suitable boundary clamping conditions is discussed.

Multiscale modeling of growth plate cartilage mechanobiology.

Growth plate chondrocytes are responsible for bone growth through proliferation and differentiation. However, the way they experience physiological loads and regulate bone formation, especially during the later developmental phase in the mature growth plate, is still under active investigation. In this study, a previously developed multiscale finite element model of the growth plate is utilized to study the stress and strain distributions within the cartilage at the cellular level when rapidly compressed to 20%. Detailed structures of the chondron are included in the model to examine the hypothesis that the same combination of mechanoregulatory signals shown to maintain cartilage or stimulate osteogenesis or fibrogenesis in the cartilage anlage or fracture callus also performs the same function at the cell level within the chondrons of growth plate cartilage. Our cell-level results are qualitatively and quantitatively in agreement with tissue-level theories when both hydrostatic cellular stress and strain are considered simultaneously in a mechanoregulatory phase diagram similar to that proposed at the tissue level by Claes and Heigele for fracture healing. Chondrocytes near the reserve/proliferative zone border are subjected to combinations of high compressive hydrostatic stresses ([Formula: see text]MPa), and cell height and width strains of [Formula: see text] to [Formula: see text] respectively, that maintain cartilage and keep chondrocytes from differentiating and provide conditions favorable for cell division, whereas chondrocytes closer to the hypertrophic/calcified zone undergo combinations of lower compressive hydrostatic stress ([Formula: see text]MPa) and cell height and width strains as low as [Formula: see text] to +4%, respectively, that promote cell differentiation toward osteogenesis; cells near the outer periphery of the growth plate structure experience a combination of low compressive hydrostatic stress (0 to [Formula: see text]MPa) and high maximum principal strain (20-29%) that stimulate cell differentiation toward fibrocartilage or fibrous tissue.

Topological semimetal to insulator quantum phase transition in the Zintl compoundsBa2X(X=Si,Ge)

By first-principles calculations, we find that Ba2X(X=Si, Ge) hosts a topological semimetal phase with one nodal ring in the kx=0 plane, which is protected by the glide mirror symmetry when spin-orbit coupling (SOC) is ignored. The corresponding drumheadlike surface flat band appears on the (100) surface in surface Green function calculation. Furthermore, a topological-semimetal-to-insulator transition (TSMIT) is found. The nodal line semimetal would evolve into topological insulator as SOC is turned on. The topologically protected metallic surface states emerge around the Gamma=0 point, which could be tuned into topologically-trivial insulator state by more than 3% hydrostatic strain. These results reveal a new category of materials showing quantum phase transition between topological semimetal and insulator, and tunability through elastic strain engineering.

Effect of Strain Field on Threshold Displacement Energy of Tungsten Studied by Molecular Dynamics Simulation**Supported by the National Natural Science Foundation of China under Grant Nos 11375242, 91026002, 91426301 and 11405231, the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant No XDA03010301. WS and RJK acknowledge the support of the Office of Fusion Energy Sciences, U.S.

The influence of strain field on defect formation energy and threshold displacement energy (Ed) in body-centered cubic tungsten (W) is studied with molecular dynamics simulation. Two different W potentials (Fikar and Juslin) are compared and the results indicate that the connection distance and selected function linking the short-range and long-range portions of the potentials affect the threshold displacement energy and its direction-specific values. The minimum Ed direction calculated with the Fikar potential is 〈100〉 and with the Juslin potential is 〈111〉. Nevertheless, the most stable self-interstitial configuration is found to be a 〈111〉-crowdion for both the potentials. This stable configuration does not change with the applied strain. Varying the strain from compression to tension increases the vacancy formation energy while decreases the self-interstitial formation energy. The formation energy of a self-interstitial changes more significantly than a vacancy such that Ed decreases with the applied hydrostatic strain from compression to tension.

Effect of strain field on displacement cascade in tungsten studied by molecular dynamics simulation

Using atomistic methods, the coupling effect of strain field and displacement cascade in body-centered cubic (BCC) tungsten is directly simulated by molecular dynamics (MD) simulations at different temperatures. The values of the hydrostatic and uniaxial (parallel or perpendicular to primary knock-on atom (PKA) direction) strains are from −2% to 2% and the temperature is from 100 to 1000K. Because of the annealing effect, the influence of strain on radiation damage at low temperature has been proved to be more significant than that at high temperature. When the cascade proceeds under the hydrostatic strain, the Frenkel Pair (FP) production, the fraction of defect in cluster and the average size of the defect cluster, all increase at tensile state and decrease at compressive state. When the cascade is under uniaxial strain, the effect of strain parallel to PKA direction is less than the effect of hydrostatic strain, while the effect of strain perpendicular to PKA direction can be negligible. Under the uniaxial strain along 〈111〉 direction, the SIA and SIA cluster is observed to orientate along the strain direction at tensile state and the uniaxial compressive strain with direction perpendicular to 〈111〉 has led to the similar preferred nucleation. All these results indicate that under irradiation, the tensile state should be avoided for materials used in nuclear power plants.

The structural, electronic, magnetic and mechanical properties of quaternary Heusler alloys ZrTiCrZ (Z = Al, Ga, In, Si, Ge, Sn): a first-principles study

The structural, electronic, magnetic and mechanical properties of the quaternary Heusler alloys ZrTiCrZ (Z = Al, Ga, In, Si, Ge, Sn) have been investigated firstly by using the first-principles calculations. The preferred configurations of the ZrTiCrZ alloys are all Y-type (I). At their equilibrium lattice constants, the ZrTiCrZ alloys are half-metallic (HM) ferrimagnets for Z = Al, Ga and In, while spin-gapless semiconductor (SGS) antiferromagnets (AFM) for Z = Si, Ge and Sn. The total magnetic moments of the ZrTiCrZ alloys are −1 for Z = Al, Ga and In, while 0 for Z = Si, Ge and Sn, both linearly scaled with the total number of valence electrons by Slater–Pauling rule . The elastic constants , and of the single crystal and the related elastic moduli , , , and of the polycrystalline aggregates are also calculated and used to study the mechanical stability of these alloys. Although the Curie temperatures of the ZrTiCrZ alloys are overestimated by using the mean field approximation (MFA), they can be better estimated by including the exchange interactions. Finally, the HM stabilities as well as the total and atomic magnetic moments of the ZrTiCrZ alloys (Z = Al, Ga, In) under either hydrostatic strain or tetragonal strain are also discussed.

Hydrogen induced amorphisation around nanocracks in aluminium

The environment generally increases the rate of fatigue crack growth in aluminium alloys by an order of magnitude due to environmental moisture that dissociates on the fracture surface to release atomic hydrogen causing some form of hydrogen assisted cracking or embrittlement. However, to date there is still uncertainty in the mechanism by which hydrogen increases the rate of crack growth. To further investigate this, classical molecular dynamic simulations were performed on a nanoscale crack in a block of pure aluminium with two hydrogen pre-charged configurations, namely, in-plane and adsorbed atomic hydrogen subjected to either cyclic unidirectional and hydrostatic strains. It was found that in-plane hydrogen combined with high stress produced a hydrogen filled amorphous zone at the crack tip resulting in quasi-cleavage like separation. Our results reveal that the production of the amorphous zone under cyclic loading significantly increased the rate of crack growth, indicative of hydrogen embrittlement, while adsorbed hydrogen had little effect on the extension of these nanocracks.

Prediction of topological insulators in supercubane-like materials based on first-principles calculations

The lattice structures and topological properties of (X = C, Si, Ge, Sn, Pb) under hydrostatic strain have been investigated based on first-principle calculations. Among the materials, , , and are dynamically stable with negative formation energy and no imaginary phonon frequency. We find that the hydrostatic strain cannot induce a quantum phase transition between topological trivial and nontrivial state for both and , while for and the tensile strain can play a unique role in tuning the band topology, which will lead to a topological nontrivial state with Z2 invariants (1;111). Although the topological transition occurs above the Fermi level, the Fermi level can be tuned by applying electrostatic gating voltage.

Influence of pressure on the properties of GaN/AlN multi-quantum wells – Ab initio study

Pressure dependence of physical properties of GaN/AlN multi-quantum wells (MQWs) was investigated using ab intio calculations. The influence of pressure was divided into two main contributions: pressure affecting the properties of GaN and AlN bulk semiconductors and an influence on systems of polar quantum wells deposited on various substrates. An influence of hydrostatic, uniaxial, and tetragonal strain on the crystallographic structure, polarization (piezoelectricity), and the bandgap of the bulk systems is assessed using ab initio calculations. It was shown that when a partial relaxation of the structure is assumed, the tetragonal strain may explain an experimentally observed reduction of pressure coefficients for polar GaN/AlN MQWs. The MQWs were also simulated directly using density functional theory (DFT) calculations. A comparison of these two approaches confirmed that nonlinear effects induced by the tetragonal strain related to lattice mismatch between the substrates and the polar MQWs systems are responsible for a drastic decrease of the pressure coefficients of photoluminescence (PL) energy experimentally observed in polar GaN/AlGaN MQWs.

The structural, electronic and magnetic properties of quaternary Heusler alloy TiZrCoIn

Abstract Employing the first-principles calculations, we have investigated the structural, electronic and magnetic properties of quaternary Heusler alloy TiZrCoIn. The TiZrCoIn alloy with type (I) configuration is predicted to be half-metallic ferromagnet at its equilibrium lattice constant 6.525 A with an indirect band gap of 0.930 eV in minority spin channel. The total magnetic moment is 2 μ B /f.u., following the Slater–Pauling rule μ t =Z t −18. Moreover, the negative formation energy indicates the thermodynamical stability of this alloy. The band gap of minority spin channel is determined by the bonding (t 2g ) and antibonding (t 1u ) states created from the hybridizations of the d states of transition metal atoms Ti, Zr and Co. In addition, the HM, character is kept as hydrostatic strain ranged from −10% to 7.6% and tetragonal strain ranged from −19% to 27%.

Computational characterization of fracture healing under reduced gravity loading conditions.

The literature is deficient with regard to how the localized mechanical environment of skeletal tissue is altered during reduced gravitational loading and how these alterations affect fracture healing. Thus, a finite element model of the ovine hindlimb was created to characterize the local mechanical environment responsible for the inhibited fracture healing observed under experimental simulated hypogravity conditions. Following convergence and verification studies, hydrostatic pressure and strain within a diaphyseal fracture of the metatarsus were evaluated for models under both 1 and 0.25 g loading environments and compared to results of a related in vivo study. Results of the study suggest that reductions in hydrostatic pressure and strain of the healing fracture for animals exposed to reduced gravitational loading conditions contributed to an inhibited healing process, with animals exposed to the simulated hypogravity environment subsequently initiating an intramembranous bone formation process rather than the typical endochondral ossification healing process experienced by animals healing in a 1 g gravitational environment. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1206-1215, 2016.

Anomalous lattice deformation in GaN/SiC(0001) measured by high-speed in situ synchrotron X-ray diffraction

We report an anomalous lattice deformation of GaN layers grown on SiC(0001) by molecular beam epitaxy. The evolution of the lattice parameters during the growth of the GaN layers was measured by in situ synchrotron X-ray diffraction. The lattice parameters in the directions parallel and normal to the surface showed significant deviation from the elastic strains expected for lattice-mismatched films on substrates up to a thickness of 10 nm. The observed lattice deformation was well explained by the incorporation of hydrostatic strains due to point defects. The results indicate that the control of point defects in the initial stage of growth is important for fabricating GaN-based optoelectronic devices.

Robust half-metallic properties in inverse Heusler alloys composed of 4d transition metal elements: Zr2RhZ (Z=Al, Ga, In)

A first-principles approach is used to study the electronic and magnetic properties of Zr2RhZ (Z=Al, Ga, In) alloys in the Hg2CuTi-type structure. The Zr2RhZ (Z=Al, Ga, In) alloys are found to be half-metallic ferrimagnets. The half-metallicity is quite robust against hydrostatic strain and tetragonal deformation in Zr2RhZ (Z=Al, Ga, In) alloys. The magnetization of Zr2RhZ (Z=Al, Ga, In) alloys mainly originates from the 4d electrons of Zr atoms and follows the rule: Mt=Zt−18. Zr2Rh-based alloys do not contain any 3d transition metal element, which implies a wider field to search for new half-metallic materials.

A large-scale simulation method on complex ternary Li–Mn–O compounds for Li-ion battery cathode materials

To meet the requirement of large-scale simulation technics for Li-ion battery electrode materials, we introduce the charge-transfer modified embedded-atom method (CT-MEAM) in which the complex nature of the chemical bonding in transition metal (TM) oxides is described as a balance between metallic/covalent and ionic contributions by MEAM and a variable-charge model, respectively. The method is applied to Li2MnO3, and the parameterization is performed through fitting the energy–strain curves of Li2MnO3 under uniaxial, biaxial and hydrostatic strains to a training set from ab initio density-functional theory calculations. The CT-MEAM prediction of the critical physical properties such as charge states and redox potentials match quite well with the ab initio results in various Li–Mn–O compounds beyond Li2MnO3. The constructed Li–Mn–O phase diagram is also qualitatively consistent with the ab initio reference work. The excellent transferability ensures use of the present method for a wide range of oxidation states in complex ternary TM oxides. Therefore, it will facilitate large-scale atomistic calculations required for the optimal design of many TM oxide applications including lithium-ion battery cathode materials.

TMIC-12MODELING AND ESTIMATION OF TUMOR INTERSTITIAL FLUID PRESSURE AND NORMAL TISSUE COMPRESSION USING HYPERFOAM THEORY AND FINITE ELEMENT TECHNIQUE

TMIC-12. MODELING AND ESTIMATION OF TUMOR INTERSTITIAL FLUID PRESSURE AND NORMAL TISSUE COMPRESSION USING HYPERFOAM THEORY AND FINITE ELEMENT TECHNIQUE Narsollah Goudarzi1, Reza Faghihi1, James Ewing2, Brent Griffith2, David Nathanson2, Ali Arbab3, and Hassan Bagher-Ebadian2,4; Shiraz University, Shiraz, Fars, Iran; Henry Ford Hospital, Detroit, MI, USA; Georgia Regents University, Atlanta, GA, USA; Oakland University, Rochester, MI, USA Recent studies have shown that mechanical stresses and interstitial fluid pressure (IFP) gradients of solid and embedded tumors directly contribute to their aggressiveness and response to therapy. Thus, studying and modeling these parameters play an important role in diagnosis and therapy of solid tumors. In this study, a mathematical benchmark was developed based on the IF flow, conservation laws for mass and momentum, and hyperfoam theory to model a physiological system containing a solid tumor surrounded by normal tissue. Using a finite element technique, IFP and tissue compression weremodeled fora solid tumor with diameterof 20 mmsurroundedbynormal tissue with thickness of 20 mm. It was hypothesized that the normal tissue can experience elastic and plastic phases during the compression. Hyperelastic parameters of white-matter were recruited in the hyperfoam strain energy function for modeling the distribution of tumor pressure load to its surrounded normal tissue, tumor, and normal IF velocities as well as displacement, stress, strain, and Young modulus of the normal tissue. Results imply that the IFP is highest and almost uniform inside the tumor and due to the small IFP gradient inside the tumor, the IF velocity is almost zero inside the tumor but high in its adjacent normal tissue while it drops abruptly in the normal tissue. Normal tissue displacement is high close to the boundary of the tumor and deceases with distant from tumor boundary. Stress distribution and Young’smodulus in normal tissue arealmostuniform while the hydrostatic strain is highclose to the boundaryof the tumorand decreases smoothly with distant from tumor boundary. This pilot study provides a practical benchmark for characterizing the mechanical properties of embedded tumors and their surrounded normal tissues that are considered as useful information in studying the embedded tumors in research and clinic. Neuro-Oncology 17:v221–v225, 2015. doi:10.1093/neuonc/nov236.12 Published by Oxford University Press on behalf of the Society for Neuro-Oncology 2015.

Reduction of the Mg acceptor activation energy in GaN, AlN, Al0.83Ga0.17N and MgGa δ-doping (AlN)5/(GaN)1: the strain effect

To resolve the p-type doping problem of Al-rich AlGaN alloys, we investigate the influence of biaxial and hydrostatic strains on the activation energy, formation energy and band gap of Mg-doped GaN, AlN, Al0.83Ga0.17N disorder alloy and (AlN)5/(GaN)1 superlattice based on first-principles calculations by combining the standard DFT and hybrid functional. We find that the Mg acceptor activation energy , the formation energy and the band gap decrease with increasing the strain ε. The hydrostatic strain has a more remarkable impact on and than the biaxial strain. Both and have a linear dependence on the hydrostatic strain. For the biaxial strain, shows a parabolic dependence on ε if while it becomes linear if . In GaN and (AlN)5/(GaN)1, parabolically depends on the biaxial compressive strain and linearly depends on the biaxial tensible strain. However, the dependence is approximately linear over the whole biaxial strain range in AlN and Al0.83Ga0.17N. The Mg acceptor activation energy in (AlN)5/(GaN)1 can be reduced from 0.26 eV without strain to 0.16 (0.22) eV with the hydrostatic (biaxial) tensible strain 3%.

A reformulation of constitutive relations in the strain gradient elasticity theory for isotropic materials

• The Abstract and the Conclusion parts have been rewritten and polished. • The use of the English language has been improved with the help of the language editing service. • The research objectives and procedures are presented more clearly in the revised manuscript. The general isotropic strain gradient elasticity theory with five higher-order elastic constants is reformulated by introducing two different orthogonal decompositions of the strain gradient tensor. Just applying the mathematical reformulations, no extra conditions needed, the constitutive relations, equilibrium equation and boundary conditions are reformulated. In the reformulated theory, the number of independent higher-order elastic constants is proved to be three for isotropic materials, which indicates that the five higher-order elastic constants in the general isotropic strain gradient elasticity theory are dependent with each other. Therefore, the general strain gradient elasticity theory contains only three independent material length-scale parameters for isotropic materials in addition to the Lame constants. The new theory is different from the existed strain gradient elasticity theory with one or three material length-scale parameters, which introduces extra conditions during deriving process. Moreover, the reformulated theory can be directly reduced to that of incompressible materials by assuming the terms associated with hydrostatic strains to be zero. Some examples, such as torsion of cylindrical bars, shearing of fixed-end layers, and pure bending of thin beams, are performed to reveal the necessity of including multi-length-scale parameters in the strain gradient elasticity theory to predict size effects at micron scale.

Structural, optical, electrical properties, and strain/stress of electrochemically deposited highly doped ZnO layers and nanostructured ZnO antireflective coatings for cost-effective photovoltaic device technology

High quality polycrystalline and nanostructured ZnO thin films were electrochemically deposited from aqueous solution of zinc nitrate (Zn(NO3)2) at negative electrochemical potential (EC=−0.6 to ‑−1.4V) and moderate temperature (75–80°C) on various substrates (Cu, Si, Mo/glass, ZnSe/Mo/glass, F:SnO2/glass). Undoped (i-ZnO) films were grown free of strain on Cu and Mo/glass using intermediate lattice matched buffer (ZnSe). The i-ZnO films on Si exhibited high tensile in-plane stress of σ=4GPa. Growth rates depended on substrate orientation and electrochemical potential varying from EC=−1.1V for deposition on Si(100) to EC=‑−1.3V for optimum deposition on Si(111). Growth rates of undoped and doped (n-ZnO) films with Al and In dopant (Al:ZnO, In:ZnO) on Mo/glass depended on the solute dopant (AlCl3, InCl3) concentration (0.2nm/s for i-ZnO, 0.7nm/s for n-ZnO with n=5mM, 1.2nm/s for n-ZnO with n=9mM). Hydrostatic compressive strains by incorporation of 0.4–12.0 at.% Al were in the range of εh=‑−0.070 to ‑−2.000. The resistivity of metal-pin contacted n-ZnO/i-ZnO films (Me/Al:ZnO/i-ZnO/Mo/glass, Me/In:ZnO/i-ZnO/ZnSe/Mo/glass, Me: Au/Ni) was in the order 105Ω·cm. In the UV–VIS-NIR region (1.5–5.0eV), the reflectivity of the films did not exceed 20% and the (optical) band gap of Eg=3.5eV indicated their high optical quality and material purity. The optical properties of electrochemically grown ZnO nanorod arrays (transparency: 70-80% at 1.5-3.0eV and band-gap: 3.3–3.7eV) were additionally analyzed by photoreflectance spectroscopy. By application of optical modulation techniques, both spectrally (4meV at 300K) and spatially (7meV/cm) resolved gap energies were quantified and the role of nitric (HNO3) and nitrate (NH4NO3) additives was extensively reinforced. Antireflective coatings (ARCs) of ZnO nanorods assembled in Cu(In,Ga)Se2 thin film solar cells were found to quench the surface reflectivity by 5% at least. Integration of electrochemically processed transparent conductive ZnO films and ZnO ARCs in solar cell device technology is anticipated to provide key-solutions for cost effective energy harvesting.

Effects of ultraviolet-assisted electrochemical etching current densities on structural and optical characteristics of porous quaternary AlInGaN alloys

Effects of ultraviolet-assisted photo-electrochemical (PEC) etching current densities (J=20, 40, 80, and 160mA/cm2) towards structural, physical, and optical properties of aluminium indium gallium nitride (AlInGaN) semiconductors as well as corresponding schematized mechanism were studied and discussed. Formation of porous AlInGaN semiconductors at J lower than 80mA/cm2 has led to the acquisition of larger lattice parameters c and a, out-of-plane strain, in-plane strain, and hydrostatic strain as compared to the non-porous semiconductor, owing to the generation of more vacancy-type defects in the porous AlInGaN semiconductors. For the porous semiconductor formed at J greater than 80mA/cm2, the etching was affected by a limited mass transport of electrons and holes for anodic oxidation and cathodic reduction. According to the band gap (Eg) and Urbach energy (UE) determined from photoluminescence (PL) shift and UV–Vis absorption measurement, the vacancy-type defects were revealed as the radiative localized states that led to the enhancement in PL peak intensity. The acquisition of a lower density of dislocation-type defects in the porous semiconductors in contrast to the non-porous one on the other hand indicated that the dislocations were the non-radiative recombination centres, in which much of the density has been eliminated after PEC etching in the 1% potassium hydroxide electrolyte.